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Abstract
A deferred antagonism method was used to test 181 Streptococcus, 47 Enterococcus and 49 Lactobacillus isolates for production of bacteriocin-like inhibitory activity against eight mutans streptococci indicator strains. Inhibitor testing was carried out on blood agar medium (BA) and also on BA which had been supplemented with 0.5 per cent calcium carbonate (BA + Ca) to minimise pH-related inhibitory effects due to the accumulation of acidic metabolites. The streptococci tested for anti-mutans activity included 54 strains representing 16 different Lancefield serological groups. Eight of these strains (3 group A, 1 group B and 4 group C) were inhibitory to mutans streptococci on BA + Ca medium. Of the 127 non-Lancefield grouped streptococci, only one of 28 S. milleri, four of 28 mutans streptococci and two of each of 17 S. uberis and 21 S. salivarius isolates were inhibitor-positive on BA + Ca. All 49 tested lactobacilli appeared to be inhibitor-negative. One of eight Enterococcus faecium and 31 of the 39 Efaecalis isolates displayed anti-mutans activity. However, all of the inhibitory E. faecalis were also protease-positive and it is haematin, formed by the proteolytic digestion of haemoglobin, that accounts for their inhibitory activity on blood-containing medium. If this haematin-related activity is disregarded, only 6.5% of the 277 strains had bacteriocin-like anti-mutans activity on BA + Ca medium. The results of this survey indicate that the production of bacteriocins inhibitory to mutans streptococci may be an uncommon characteristic of streptococci, enterococci and lactobacilli.